Remote control system



June l0, 1941. H, Q PETERSON 2,244,725

REMOTE CONTROL SYSTEM Original Filed June .19, 1935 AVC INVENTOR ATTORNEY Patented June l0, 1941 REMOTE CONTROL SYSTEM Harold 0. Peterson, Riverhead, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Original application June 19, 1935, Serial No. 27,319. Divided and this application May 26, 1939, Serial No. 275,785

(Cl. Z50-40) 4 Claims.

This application is a division of my copending application Serial No. 27,319, filed June 19, 1935, which issued July ll, 1939 as U. S. Patent #2,165,502. Y

The present invention relates to receiving systems, and particularly to such of these as may be controlled from a remote point. The species of the invention as herein shown and claimed was shown but not claimed in the parent application.

In present commercial radio communications practice, the radio receiver is usually situated at a location particularly free from local disturbances and chosen for its good conditions of reception. For the sake of expediency in the handling of trame, the operator is usually situated at a central oice located in the city or at a point conveniently accessible to the consumers of the service rendered. As an example, one of the large communication companies has built a receiving station at Riverhead, New York, where receiving conditions are particularly good. However, the operator who copies the signals is situated in a central office in New York city. The function of the receiving station at Riverhead is merely to select the desired radio signal, amplify it, and convert it to a form of electrical energy suitable for transmission over a connecting link between Riverhead and New York, this connecting link being, in this case, a pair of Wires in a telephone cable. At present, the receiving apparatus at Riverhead is maintained in proper adjustment by men stationed at Riverhead, who receive instructions over an order wire. Due to drifts in transmitter frequency and diurnal variations of signal intensity, it is usually necessary for the receiver attendant at Riverhead to make numerous adjustments of his receiver during the course of a day.

An object of the present invention is to enable the operator at the central oflice to make the most important of the adjustments necessary at the remote receiver, thus relieving the receiver attendant of a considerable portion of his work.

The two major adjustments required to be made on a receiver after it has been tuned to a given circuit are gain control and heterodyne frequency control. With the degree of frequency stability now attained in modern transmitters, it should not be necessary to retune the radio frequency amplifier stages of the receiver during the course of a days running on a given channel. In the system of the present invention, it is proposed to adjust the receiver gain by means of an automatic volume control arrangement,

while the heterodyne frequency control is manipulated through remote control mechanism by the operator at the central oflice, whereby the adjustment may be maintained at all times at a point which gives best results.

A better understanding of the invention may be had by referring to the following description which is accompanied by a drawing the sole figure of which illustrates a preferred embodiment of the invention.

The drawing shows a schematic diagram of the complete system. The signal is received on antenna I and amplified by radio frequency amplifier 2. A heterodyne detector unit 4 converts the signal to an audio frequency beat note. The heterodyne oscillator of this unit may be varied over a desired band of frequencies by means of trimmer condenser 3. The beat note is amplied in amplifier 5 and passed through a low pass lter 6 which has a cut-off frequency approximately the same as that of the tone line I5 over which the signal is transmitted to the central office. In the case of loaded cables, the connecting link may have a cut-off at approximately 2300 cycles. After passing through 10W pass filter 6, the signal is fed into the connecting link I5 through a level control network 1, from which the signal is supplied to a suitable recording device, herein shown by way of example as a headset I4. Signal voltage from the output of low pass filter 6 is also impressed on the grid of rectifier tube 8, which is normally biased to cut-01T. The signal applied to detector tube 8 causes it to draw plate current through resistances 9 and I0, thus producing a voltage drop which charges condenser I3 through resistance II and impresses a negative voltage on the control grids of radio amplifier 2, consequently affording a way of maintaining the output level of the receiver substantially constant irrespective of input signal strength.

In telegraph communications, the carrier is absent between characters, and, consequently, if no signal is transmitted between messages, the receiver will be caused to assume a condition of maximum gain by virtue of the automatic volume control arrangement. To enable the receiver to re-adjust itself with maximum speed as soon as transmission is resumed, there is provided an electronic device I2 in parallel with the time constant resistor II. The functioning of this device is adequately described in my Patent No. 2,093,095, dated September 14, 1937, and has been found in practice to greatly improve the performance of this type of receiver.

The heterodyne frequency control is controllable at the central oflice in the form of two push buttons 3| and 32, one of which causes a current of selective characteristics to flow over the control line 29, and the other of which causes a current of differently selective characteristics to flow over said line. At the receiving station this current is responded to after filtering, amplifying and rectification by a relay system which controls a flexible shaft I6 rotated by a motor I8 in a manner such as to provide reversible adjustment of the frequency determining element 3 in the heterodyne receiver. If the operator at the central office pushes one of the buttons 3| or 32, the armature of the actuated relay 58 or 60 closes a circuit through one of the two electromagnet coils I9 or 20 which causes theV rotating shaft I6 from motor I8 to engage with one side of a groove in the wheel 2|, causing that wheel to rotate and drive the frequency controlling condenser 3 through reduction gears 23 and 22. The manner in which the rotating shaft from motor I8 may engage wheel 2| is described in great detail in U. S. Patent No. 2,184,958, granted December 26, 1939 to De Witt R. Goddard.

The drawing further illustrates a method whereby one voice frequency carrier channel can be used for obtaining two different effects. In this system the voice frequency carrier channel is periodically interrupted, or keying at one of two discrete interrupting frequencies which is selected at the receiving station by a resonant device such as, for instance, a vibrating reed type of relay. By way of illustration assume that the voice frequency carrier channel used is 425 cycles. The keying frequencies may be 2O cycles and 30 cycles provided by alternators or generators 50 and 5I. When the receiving operator Wishes to make an adjustment, he may depress push-button 32, which closes keying frequency generator D in series with a battery through the coil of relay 52, causing the contacts of relay 52 to open and close at the frequency generated by 50. In this Way periodic impulses of 425 cycle voltage from generator 53 are transmitted through transformer 54 and sending filter 55 into the connecting link 29. The impulses are selected by receiving filter 56, and then amplified and rectified by the ampli- Iier rectifier unit 51. Thus, the control energy appears as pulsating direct current through the coil of relay 58. The armature of this relay may be of a vibrating reed construction so proportioned as to resonate at the frequency generated by 50, in which case the armature will vibrate at sufficient amplitude to strike the contacts of relay 58 and cause control current to flow through electromagnet I9. Similarly, if control in the opposite direction is desired, push button 3| would be depressed, sending a different keying frequency into relay 59 which interrupts the 425 cycle tone and passes it out over the same circuit to be converted to pulsating direct current at a proper frequency to cause the armature of tuned relay 60 to vibrate and eventually to energize electromagnet 2U. In this circuit it is not necessary to have separate relays 52 and 59, it being possible to connect both generators 50 and 5| to the battery through the coil of one relay.

It is to be understood, of course, that the invention is not limited to the precise details shown and described since various other types s of mechanism Inlay be used Without departing from the spirit and scope thereof; for example, this type of control mechanism can also be applied to the adjustment of other parts of the receiver or to the adjustment of other apparatus such as transmitters.

What is claimed is:

1. In a commercial radio telegraph communication system, a heterodyne receiver for receiving signal waves, a remote control station, utilization apparatus at said remote control station, a wire line extending between said utilization apparatus and said receiver, said line being coupled to the output of said receiver, and means for controlling the heterodyne frequency at said receiver, said means including tuning mechanism at said receiver, a normally open-circuited tone frequency generator, and two generators of oscillations of different keying frequencies at said control station, a wire circuit extending from said control station to said tuning mechanism, relay means at said control station selectively operable at either of said keying frequencies for closing the circuit of said tone frequency generator and for effecting the transmission of periodically keyed oscillations therefrom over said circuit in accordance with a selected one of said keying frequencies, two single filters, one at said control station and the other at said receiver for passing the oscillations generated by said tone frequency generator, means for rectifying the tone frequency energy passed by said filters, thereby to derive impulses of said keying frequencies, individual relays at said receiver each resonantly operable in response to an appropriate one of said keying frequencies, means operative under control of a selected one of said relays for adjusting said tuning mechanism, and keying mechanism for selectively operating said relays at the control station, whereby said tuning mechanism at said receiver may be controlled in either of two senses.

2. Remote control apparatus for an adjustable element of a radio receiver, comprising a station remote from said receiver, said station having sources of electric Waves of two different, but relatively low frequencies, a tone frequency generator, means for selectively modulating the output of said generator by either one of said low frequencies at will, a communications channel extending from said station to said receiver and adapted to translate signals produced by the modulation of said generator output, a rectifier adjacent said receiver for demodulating said signals, motor driven means for effecting adjustment of said adjustable element in said receiver in either of two senses, and means selectively responsive to signals of one or the other of said two low frequencies for determining the sense of the adjustment of said element, the duration of the selected signal being determinative of the extent of said adjustment.

3. Remote control apparatus, according to claim 2, and having a filter at each end of said communications channel, each filter being adapted to pass the modulated tone frequency of said signals.

4. Remote control apparatus, according to claim 2, and having manually operable means for selecting the desired one of said sources of low frequency waves for modulating the output from said tone frequency generator, the last said means being adapted to permit a continuous transmission of the selected signal until a desired adjustment of said adjustable element has been effected.

HAROLD O. PETERSON. 

